Kockney Koi 8mm–4mm–8mm Airline Reducing T-Pieces – Pack of 3

Kockney Koi Airline Reducing T-Pieces – 8mm × 4mm × 8mm

Add a smaller airline branch while keeping an 8mm main run

The Kockney Koi Hi-Flow Airline Reducing T-Piece connects two 8mm airline sections with a smaller 4mm branch. It is useful when an aeration layout needs a small spur from a larger air line, without reducing the whole run to 4mm. Supplied as a pack of three, these fittings give you matching connectors for several branching points or a spare for future changes.

The connection sizes describe the layout: 8mm at each end of the straight section and 4mm on the side branch. This is different from an equal tee, where all three connections are the same size, and from a straight reducer, which joins only two hoses. Choose the shape that matches the route you actually need to build.

Specifications at a glance

Product	Kockney Koi Hi-Flow airline reducing T-piece
Main connections	8mm and 8mm
Branch connection	4mm
Pack quantity	3 fittings
Manufacturer reference	010123
Connection style	Barbed airline connections

Where a reducing tee is useful

A mixed-size airline layout may be appropriate when the main route uses 8mm hose and a nearby accessory takes a 4mm connection. The tee allows that smaller branch to be taken from the main run. Before adding it, check the air requirement of the accessory and the capacity of the pump, as a connector cannot create additional air output.

For example, if you already have an 8mm airline serving an aeration point and want a separate 4mm feed, a reducing tee provides the physical junction. Whether the resulting arrangement delivers enough air to both points depends on the pump, hose lengths, diffuser resistance and water depth. Plan those details together instead of assuming that every branch will receive an equal share.

Select the correct airline sizes

Check the internal bore of the hose you are connecting. Airline is often listed with both an internal and external diameter, and confusing those measurements can result in a loose or excessively tight connection. The larger ends of this fitting are intended for the 8mm airline run; the smaller branch is for 4mm airline. Do not force an unsuitable size over a barb.

Our standard sinking airline includes 4mm and 8mm options, allowing you to select the appropriate size for each part of the junction. For a heavier underwater hose, see the matching sizes in our Evolution Aqua heavy-duty sinking airline range. Check the exact option and length before adding it to your order.

Black braided airline is another option for suitable air installations, but it does not sink. If you use it below the water surface, plan how it will be secured. Choosing a dark hose for appearance and choosing a weighted hose for its behaviour in water are separate decisions.

Planning airflow through the branches

The reducing tee is an open connection, not an adjustable valve. It does not provide individual flow control or automatically balance the branches. If you need to regulate how much air each outlet receives, include compatible air-control fittings in the design and follow the pump manufacturer’s guidance. Avoid closing outlets in a way that leaves the pump working against excessive restriction.

Shorter hose runs and shallower diffusers can receive air more readily than longer runs or deeper outlets. If one diffuser appears much stronger after adding a branch, check the arrangement as a whole. The cause may be the difference in resistance between branches rather than a defective tee. Keep hose routes reasonably direct and avoid kinks that can restrict delivery.

Fitting and checking the connections

Plan the tee’s position before cutting the airline. Leave enough room around the junction to fit the hoses securely and to inspect them later. Make clean, square cuts in sound tubing, and push each hose onto its correct connection. Check that the ends are seated and supported so that the weight or movement of the hose does not pull on the fitting.

After reconnecting the system, check air delivery at every affected diffuser or accessory. Look for loose connections and make sure the new branch has not caused another outlet to stop receiving air. If you move equipment later, repeat these checks. A useful layout is one that can be inspected and maintained without dismantling unrelated parts of the pond system.

Choosing between tees, reducers and check valves

An equal tee is intended for a junction where all three connections use the same airline bore. A straight reducer is more suitable when changing hose size without adding a branch. This reducing tee is the choice when you need two 8mm connections and one 4mm connection together. Check the connection layout before ordering, rather than choosing solely from a photograph of a similar fitting.

Backflow protection is a separate consideration. The tee does not prevent water moving backwards through an airline when the pump stops. Follow your air pump’s installation guidance, including its position relative to the water and any requirement for non-return valves. The pack contains three reducing tees; airline, pumps, diffusers and additional valves are supplied separately.